Apparatus and method for processing optical information using low
density parity check code

ABSTRACT

An apparatus and method for processing optical information using a low density parity check code are suggested. An optical information recording method includes the steps of encoding data to record into a low density parity check code; representing the data, which is encoded into the low density parity check code, to a spatial light modulator in the unit of a data page; and modulating a recording beam into the data page representing the spatial light modulator to be recorded in the form of hologram in a recording medium. By blocking inexact probability information from being concentrated in the LDPC code block, by achieving exact probability information through effective allocation of a mark, and by improving average accuracy of the pixel, which corresponds to the LDPC code, failure rate of decoding can be minimized so that decoding performance can be improved.

TECHNICAL FIELD

The present invention relates to an apparatus and method for processingoptical information using a low density parity check code.

BACKGROUND ART

An optical information processing apparatus using the holography is akind of page-oriented memories and uses a parallel signal processing asan input/output method. Accordingly, a holographic optical informationprocessing apparatus can perform data processing faster than a CD(Compact Disk) or DVD (Digital Versatile Disk) which records orreproduces data by a bit.

An optical information processing apparatus using the holographyperforms recording operation by projecting an information beam, whichcontains an image information of data to record, and a reference beam,which is to be interfered with the in formation beam, to an opticalinformation recording medium (ex, optical data storage). In the otherhand, for reproducing, the reference beam is projected to the opticalinformation recording medium, a reproduced beam, which is diffractedfrom the recording medium, is detected by an optical informationdetector such as a CMOS (Complementary Metal-Oxide Semiconductor) or CCD(Charge Coupled Device), and original data is reproduced by signalprocessing and decoding.

However, due to variations of channel characteristic such as contractionof the optical information recording medium, the detected data page mayhave errors when an image of data page is detected by the opticalinformation detector. For example, a pixel of the data page(hereinafter, called as ‘a data pixel’) and a pixel of the opticalinformation detector (hereinafter called as ‘a detecting pixel’) may notmatch with each other due to a mis??alignment. These errors may cause afairly high bit error rate (BER).

To decrease BER, an error correction code (ECC) is introduced. AmongECCs, there is a low density parity check (LDPC) code whose performanceclose to the Shannon's theoretical limitation of the channel capacity.The LDPC code is a linear block code where most elements of the paritycheck matrix are symbol “0.”

A parity check code has a block which contains information symbols andparity check symbols which is a modulo sum of specific informationsymbols so that it constitutes a code word.

The relation between the check symbols and the information symbols canbe represented by a parity check matrix “H”. The parity check matrix Hcan be represented by a set of linear homogeneous equations. That is,LDPC code is one of parity check codes and it has a parity check matrixof which most elements are symbol “0” and the remains have randomlyscattered weights.

Encoding process of the LDPC code with the parity check matrix H isdescribed as follows. When the parity check matrix H is achieved, agenerator matrix G, which corresponds to the parity check matrix H, isgenerated by using the relation GH^(T)=0. A code word C, whichcorresponds to the information symbol block X, can be achieved from therelation C=XG. If numbers W and W×(N/M) with respect to the matrix H(H=N×M) are constant, where the number W is the number of 1 s per eachcolumn and the number W×(N/M) is the number of 1 s per each raw, it iscalled as a regular LDPC code.

If the number of is per each column is not constant and the number of isper each raw is not exactly equal to Wax (N/M), it is called as anirregular LDPC code. It is generally known that an irregular LDPC codehas better error correction capacity but it is harder to embody byhardware than a regular LDPC code.

Decoding of the LDPC code means the operation to detect the mostprobably approximate code word, which satisfies the relation where theproduct with the matrix H is equal to 0, from received signal vectors.

The sum-product algorithm among decoding methods of the LDPC codeperforms a soft decision iterative decoding using probability values.According to the sum-product algorithm, decoding is performediteratively, while massages of probability are transmitted among nodesin the code word graph, until the code word, which satisfies thecriteria of the maximum likelihood, is achieved.

There is another decoding method of LDPC code, so called LLR algorithm,which use a log-likelihood ratio (LLR). With respect to the LLRalgorithm, Korean registered patent No. 10-0538281 can be referred.

The LLR algorithm is described in brief as follows. A LDPC decodercalculates initial LLR after calculating probabilities for each casewhen the data pixel is symbol “0” or “1”.

DISCLOSURE OF INVENTION Technical Solution

An optical information recording apparatus includes; an encoding portionfor encoding data to record by using a low density parity check code; alight modulating portion for representing data, which is encoded at theencoding portion, into a data page which is configured with a pluralityof data blocks; and a beam source for projecting beam to the lightmodulating portion so that the data page represented in the lightmodulating portion is recorded at a recording medium as hologram.

The data page may include the data block and an address block.

The data block may be configured with a plurality of subblocks and amark which is located at the center of the data block.

The mark may be used as information to calculate reproductionprobability of the data block.

The encoding portion may include an encoder for encoding the data intothe low density parity check code and a mapping unit for mapping the lowdensity parity check code in the unit of the data page.

The mapping unit may map the low density parity check codes, which isencoded, at the encoding unit, into the data page after scrambling.

The data page may include the data block and address block foraddressing the data page, the data block is configured with a pluralityof subblocks and mark which is located at the center of the data block.

The low density parity check code, which is encoded at the encoder, maybe divided into a plurality of areas as many as the number of the datablocks and each area may be divided into a plurality of segments as manyas the number of the areas.

The number of the data block N (N is a positive integer), the number ofareas and the number of the subblocks may be equal to each other.

The mapping unit may map the j-th segment (j=1,2,3 . . . N) of the i-tharea (i=1,2,3 . . . N) into the (((i+j−2) mod N)+1)-th subblock of thej-th (j=1,2,3 . . . N) data block.

An optical information recording method includes encoding data into alow density parity check code; representing the data, which is encodedinto the low density parity check code, to a spatial light modulator inthe unit of a data page; and modulating a recording beam into the datapage representing the spatial light modulator to be recorded in the formof hologram in a recording medium.

The data page may include a data block in which data, which is encodedinto the low density parity check code, is mapped and an address block,which has address information of the data page.

The data block may be configured with a plurality of subblocks and amark which is located at the center of the data block.

The mark may be used as information to calculate reproductionprobability of the data block which includes the subblocks.

The low density parity check Code may be mapped into the data blockafter scrambling.

The data page may include the data block and an address block foraddressing the data page, the data block may be configured with aplurality of subblocks and a mark which is located at the center of thedata block.

The low density parity check code may be divided into a plurality ofareas as many as the number of the subblocks and each area may bedivided into a plurality of segments as many as the number of the areas.

The number of the data block N (N is a positive integer), the number ofareas and the number of the subblocks may be equal to each other.

The j-th segment (j=1,2,3 . . . N), which is one of segments included inthe i-th area (i=1,2,3 . . . N), may be mapped into the (((i+j−2) modN)+1)-th subblock of the j-th (j=1,2,3 . . . N) data block.

An optical information reproducing apparatus includes a beam source; anoptical information detecting portion for detecting the data page, whichis reproduced from a recording medium by the beam which is projectedfrom the beam source; and a decoding portion for identifying anaddressing block, detecting subblocks which is included in a data blockand a mark which is located at the center of the data block from theplurality of data blocks which is included in the data page and decodingdata of the subblock.

The decoding portion may include a demapping unit for demapping thesubblock of the data page, which is detected at the optical informationdetecting portion, and a decoder for decoding the subblock into a lowdensity parity check code by using the value that is demapped at thedemapping unit.

The decoder may perform decoding process by using probability valuewhich is calculated from the density of the data block at the demappingunit.

The density of the data block may be calculated by using the density ofthe mark.

An optical information reproducing method includes detecting a data pagewhich is reproduced from a recording medium by projection beam from alight source to the recording medium; identifying an address block whichis included in the data page; detecting a plurality of data blocks whichare included in the data page, a mark which is located at the center ofthe data block and a plurality of subblocks which are located around themark; and decoding data which is detected from the subblocks into a lowdensity parity check code. Decoding can be performed by usingprobability value which is calculated from the density of the datablocks. To calculate the probability value, the density of the mark canbe used.

The data page which is represented for processing of holographic datamay include a plurality of data blocks, a mark which is denoted at thecenter of the data block and used for reproducing, and a plurality ofsubblocks which are denoted around the mark.

The data, which is represented at the subblock, may be a low densityparity check code. The data page may include address block which isrepresented around the data block. The mark may be used as informationto calculate reproducing probability of the data block which includesthe subblocks.

In the data block, the low density parity check code can be scrambled inthe subblocks. The low density parity check code of the subblock may bedivided into a plurality of areas as many as the number of the subblocksexcept the mark and each area may be divided into a plurality ofsegments as many as the number of the areas.

The number of the data blocks N (N is a positive integer), the number ofthe areas and the number of the subblocks except the mark may be equalto each other.

The j-th segment (j=1,2,3 . . . N), which is one of segments included inthe i-th area (i=1,2,3 . . . N), may be the segment that is mapped intothe (((i+j−2) mod N)+1)-th subblock of the j-th (j=1,2,3 . . . N) datablock.

The data page for processing of holographic data according to thepresent invention includes a plurality of data blocks; a mark which isdenoted at the center of the data block and used for reproducing; and aplurality of subblocks which are denoted around the mark.

The data page may be represented to a spatial light modulator or can bedetected from an optical information detector. The data which is mappedto the subblock may be a low density parity check code. The data pagemay include an address block which is represented around the data block.

The mark may be used as information to calculate reproducing probabilityvalue of the data block which includes the subblocks.

Data in the form of the low density parity check code may be mapped tothe subblocks after being scrambled or may be the mapped one.

The low density parity check code is divided into a plurality of areasas many as the number of the subblocks except the mark and each area maybe divided into a plurality of segments as many as the number of theareas.

The number of the data block N (N is a positive integer), the number ofareas and the number of the subblocks may be equal to each other.

The j-th segment (j=1,2,3 . . . N), which is one of segments included inthe i-th area (i=1,2,3 . . . N), may be mapped into the (((i+j−2) modN)+1)-th subblock of the j-th (j=1,2,3 . . . N) data block, or may bethe segment that is mapped into the (((i+j−2) mod N)+1)-th subblock ofthe j-th (j=1,2,3 . . . N) data block.

A method for mapping a data page to a light modulator for recordingholographic data includes representing a data block by a mark, which isused for reproducing, and a plurality of subblocks, which is arrangedaround the mark; and representing the data page by the data block andthe address block.

The data, which is mapped to the subblock, may be encoded to a lowdensity parity check code. The mark may be used as information tocalculate reproducing probability of the data block.

Data, which is encoded to a low density parity code, may be mapped tothe data block after being scrambled with the subblocks.

The low density parity check code, which is mapped to the subblock, isdivided into a plurality of areas as many as the number of the subblocksexcept the mark and each area may be divided into a plurality ofsegments as many as the number of the areas.

The number of the data blocks N (N is a positive integer), the number ofthe areas and the number of the subblocks except the mark may be equalto each other.

The j-th segment (j=1,2,3 . . . N), which is one of segments included inthe i-th area (i=1,2,3 . . . N), may be mapped into the (((i+j−2) modN)+1)-th subblock of the j-th (j=1,2,3 . . . N) data block.

A decoding method of holographic data includes demapping a data page,which includes an address block, a data block and a subblock including amark, from an optical information detector which detects a reproducingbeam; and decoding the reproduced data from the data page into a lowdensity parity check code by using the mark.

The mark may be used to calculate probability value for reproducing.

Decoding into the low density parity check code may be performed byusing the density of the data block.

Advantageous Effects

The optical information processing apparatus and method using a lowdensity parity check code according to an embodiment of the presentinvention can be used to record data or reproduce data in theholographic optical information processing apparatus.

By blocking inexact probability information from being concentrated inthe LDPC code block, by achieving exact probability information througheffective allocation of a mark, and by improving average accuracy of thepixel, which corresponds to the LDPC code, failure rate of decoding canbe minimized so that decoding performance can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments will be described in detail with reference to thefollowing drawings, in which like numerals refer to like element andwherein FIG. 1 is a block diagram illustrating an optical informationrecording/reproducing apparatus according to the embodiment of thepresent invention;

FIG. 2 shows format of a data page according to the embodiment of thepresent invention;

FIG. 3 shows a mapping method of the data page according to theembodiment of the present invention;

FIG. 4 is a block diagram illustrating encoding process of data forrecording according to the embodiment of the present invention; and

FIG. 5 is a block diagram illustrating decoding process of data forreproducing according to the embodiment of the present invention.

MODE FOR THE INVENTION

FIG. 1 shows a block illustrating an optical informationrecording/reproducing apparatus.

The optical information recording/reproducing apparatus 100 includes abeam source 110, a beam splitter 120, an angle multiplexer 130, aspatial light modulator 140, an optical information detector 150, anequalizer 160, an encoding portion 170 and a decoding portion 180, asshown in FIG. 1.

Light projected from the beam source 110 is split into a reference beamR and an information beam S through the beam splitter 120. The referencebeam R goes through the first shutter 190 a and is projected to opticaldata storage at the specific angle after it is reflected at the anglemultiplexer 130.

In addition, the information beam S, where data is not loaded, goesthrough the second shutter 190 b and is projected to the spatial lightmodulator 140 after its path is changed by a reflecting mirror.

Meanwhile, the spatial light modulator 140 represents binary data, whichis received from the encoding portion 170, in the unit of data page. Theencoding portion 170 encodes original data to record into a LDPC codeand supplies it with the spatial light modulator 140 in the unit of thedata page.

The spatial light modulator 140 generates 2-dimensional image data ofthe data page by optically modulating the data page, which is suppliedfrom the encoding portion 170, and projects the data page to theincident information beam S. Accordingly, the information beam S becomesa real information beam, where data to be recorded is loaded, by passingthrough the spatial light modulator 140. After this, a signal beam,which passes through the spatial light modulator 140, is projected tothe optical data storage.

If the reference beam R and the information beam S are projected to theoptical data storage D, an interference pattern is recorded because alight induction of an internal mobile charge is generated depending onthe intensity of the interference pattern which is generated by theinterference between the reference beam R and the information beam S inthe optical data storage D.

When recording the optical information, the angle multiplexer 130controls the angle of the reference beam R, which is projected to theoptical data storage D so that angle multiplexing of the reference beamR can be realized. The angle multiplexer 130 can be embodied by arotating mirror like a galvano mirror.

For reproducing recorded data to the optical data storage D, only thereference beam R is projected to the optical data storage D. For this,the first shutter 190 a passes only the reference beam R which is splitby the beam splitter 120. Meanwhile the second shutter 190 b blocks theinformation beam S which is split by the beam splitter 120.

At this time, the reference beam R goes through the first shutter 190 aand is projected to the interference pattern, which is recorded to theoptical data storage D after being reflected by the angle multiplexer130. When the reference beam R is projected to the interference pattern,a reproducing beam, which has the image of the data page, is generatedfrom the interference pattern, which is recorded to the optical datastorage D by diffraction.

The reproducing beam is detected by the optical information detector 150in the unit of the data page. Detected data page is equalized by theequalizer 160 and decoded by the decoding portion 180.

The optical information detector 150 may be embodied by a photo detectorarray for example, CMOS (Complementary Metal Oxide Semiconductor) or CCD(Charge Coupled Device). For embodying the equalizer 160, a MMSE(Minimum Mean. Square Error) equalizer can be used.

The decoding portion 180 decodes a LDPC code. The decoding portion 180decodes a LDPC code from the equalizer 160 and outputs reproduced data.

Example of the data page will be described as follows.

FIG. 2 shows the format of the data page and FIG. 3 shows a mappingmethod of the data page.

The data page 200 includes data blocks 210 of N (N is a positiveinteger) where a LDPC code 300 (refer to FIG. 3) is mapped, addressblocks 220 of m (m is a positive integer) where addressing informationfor addressing the data page 200 for reproducing is mapped.

The data block 210 and the address block 220 have the same size “Xb×Yb”.Here, “Xb” stands for the number of pixels .in the row direction and“Yb” stands for the number of pixels in the column direction. And theaddress block 220 can be located to any location in the data page 200.

The data block includes a plurality of subblocks. The number of thesubblocks may be equal to the sum of the data blocks and the subblockswhich constitute the data page.

The subblock 212 has the size of “Xsb×Ysb.” Here, “Xsb” stands for thenumber of pixels in the row direction and “Ysb” stands for the number ofpixels in the column direction. And the number of subblocks 212 is(N+m), which is equal to the sum of the number of the data blocks 210and the number of address blocks 220 which constitute the data page 200,

A LDPC code is divided into the size of “Xsb×Ysb” and mapped into Nsubblocks among whole of the subblocks 212 individually while the mark214 is mapped into m subblocks.

The mark 214 is used to abstract information to calculate probability ofthe subblock 212 which corresponds to the data block 210 where the mark214 is belonged to. The mark 214 is located at the center of the datablock 210 and entire area of mark 214 is denoted by on-pixels oroff-pixels only.

LDPC codes, which is encoded at the encoding portion 170 in the unit ofdata page, are divided into a plurality of LDPC code areas (LDPC1,LDPC2, . . . ,LDPC N) 300, which is sized as the same as the size of thedata block 210 “Xb×Yb”. And divided LDPC code areas 300 are divided intoa plurality of segments 310 as being sized as the size of the subblock212 “Xsb×Ysb”. Accordingly, LDPC code, which is included in a segment310, can be mapped to a subblock 212. (Refer to FIG. 3)

If each LDPC code area 300 is divided into the size of the subblock 212“Xsb×Ysb,” a dividend should be a positive integer. That is, the lengthof the LDPC code should be designed to satisfy the relation“n(Xsb×Ysb)=(Xb×Yb)−m(Xsb×Ysb)”.

Refer to FIG. 3, assuming that a serial number, which is assigned toeach of the LDPC code areas 300 (LDPC1, LDPC2, . . . ,LDPCN 300), is i(i=1,2,3 . . . N) and other serial number, which is assigned to eachsegment 301 included in each LDPC code area 300 is j (j=1,2,3 . . . N),another serial number, which is assigned to each data block can bedefined by j (j=1,2,3 . . . N) as well as the serial number, which isassigned to each segment 301.

If the data of the j-th segment 301 of the i-th LDPC code area 300 ismapped into the (((i+j−2) mod N+1)-th subblock 212 of j-th data block210, segments 310 of a LDPC code area 300, which is divided into thesize of “Xsb×Ysb”, are mapped into the separate subblock 212 of theseparate data block 210 individually.

That is, segments 301, which are included in a LDPC code area 300, arescrambled and mapped to separate subblock 212 of separate data block210.

When segments 310 of a LDPC code area 300 are scrambled and mapped toseparate subblock 212 of separate data block 210, inexact informationdetected from the subblock 212 which is located far from the mark 214,can be complemented.

Encoding process and decoding process of the data page which arepeformed when optical information is recorded and reproducedindividually will be described in detail.

Each element to be referred hereinafter and explanation can beunderstood by referring to FIG. 1 through FIG. 3.

FIG. 4 is a block diagram illustrating encoding process of data forrecording and FIG. 5 is a block diagram illustrating decoding process ofdata for reproducing.

Encoding process is performed by the encoding portion 170. The encodingportion 170 includes a LDPC encoder 172 for generating a LDPC code 300by using input data and a mapping unit 174 for mapping the LDPC code300, which is generated by the LDPC encoder 172, into the data block 210and the subblock 212 of the data page 200 and mapping the address block220 and the mark 214 of the subblock 212, as shown in FIG. 4.

If data to be recorded is input, the LDPC encoder 172 encodes data intoa LDPC code 300. Generated LDPC code 300 is mapped to each subblock 212of the data block 210 by the mapping unit 174. The LDPC code 300 to bemapped to the subblock 212 will be understood through theabove-mentioned description. And all the pixels of the address block 220or the mark 214 can be mapped into on-pixel or off-pixel only

Data page 200, whose mapping operation is completed, is loaded on theinformation beam S at the spatial light modulator 140. When theinformation beam S is projected to the optical data storage D, recordinginformation of the corresponding data page 200 is recorded as aninterference pattern to the optical data storage D by the interferencebetween the information beam S and the reference beam R.

After that, decoding of data is performed by the decoding portion 180,as shown in FIG. 5.

The decoding portion 180 includes a demapping unit 182 for demapping anaddress blocks 220, data blocks 210 and subblocks 212 for reproducingthe data page 200, which is detected from the optical informationdetector 150, and for calculating probability value for decoding byusing the subblock 212 and the mark and a LDPC decoder 184 forperforming LDPC decoding by using the probability value, which isachieved at the demapping unit 182, and the density of the data block210, which is achieved from the demapped data page 200.

When reproducing the recorded optical information to the optical datastorage D, the decoding portion 180 can achieve decoding probabilityvalue and the density for LDPC decoding by using the address block 220and the mark 214 of subblock 212 so that the decoding portion 180 candecode optical information which is reproduced from the optical datastorage D.

1.-45. (canceled)
 46. A method for reproducing optical information,comprising: projecting a beam onto a recording medium that stores dataassociated with one or more low density parity check codes, wherein eachlow density parity check code is divided into a plurality of low densityparity check code segments; receiving a beam from the recording mediumincluding information in the form of a data page, wherein the data pagecomprises a plurality of data blocks, wherein the plurality of lowdensity parity check code segments are mapped within the plurality ofdata blocks to decrease the failure rate of decoding; and decoding thedata based on the one or more low density parity check codes.
 47. Themethod of reproducing optical information of claim 46, wherein the datablocks include a plurality of subblocks, and wherein the one or more lowdensity parity check codes is mapped among the subblocks.
 48. The methodof reproducing optical information of claim 47, wherein the one or morelow density parity check codes are scrambled.
 49. The method ofreproducing optical information of claim 47, wherein mapping theplurality of segments among the plurality of subblocks decreases thefailure rate of decoding by preventing inexact probability informationin the one or more low density parity check codes from beingconcentrated in a single area.
 50. A method for recording opticalinformation, comprising: encoding data into one or more low densityparity check codes; recording the data as a data page in the form ofhologram in a recording medium, wherein the data page includes aplurality of data blocks, wherein the one or more low-density paritycheck codes is divided into a plurality of segments, and wherein theplurality of segments are mapped within the data block to decrease thefailure rate of decoding.
 51. The method of reproducing opticalinformation of claim 50, wherein the data blocks include a plurality ofsubblocks, and wherein the one or more low density parity check codes ismapped among the subblocks.
 52. The method of reproducing opticalinformation of claim 51, wherein the one or more low density paritycheck codes are scrambled.
 53. The method of reproducing opticalinformation of claim 51, wherein mapping the plurality of segments amongthe plurality of subblocks decreases the failure rate of decoding bypreventing inexact probability information in the one or more lowdensity parity check codes from being concentrated in a single area. 54.An apparatus for reproducing optical information, which comprises: abeam source; an optical information detecting portion for detecting adata page, which is reproduced from the recording medium by projectingthe beam which is projected from the beam source to a recording medium,wherein the data page comprises a plurality of data blocks; and adecoding portion for detecting and decoding data within the data blocks,wherein the data blocks are encoded with data by using one or morelow-density parity check codes, wherein the one or more low-densityparity check codes are divided into a plurality of segments, and theplurality of segments are mapped within the plurality of data blocks todecrease the failure rate of decoding.
 55. The apparatus for reproducingoptical information of claim 54, wherein the data blocks include aplurality of subblocks, and wherein the one or more low density paritycheck codes is mapped among the subblocks.
 56. The apparatus forreproducing optical information of claim 55, wherein the one or more lowdensity parity check codes are scrambled.
 57. The apparatus forreproducing optical information of claim 55, wherein mapping theplurality of segments among the plurality of subblocks decreases thefailure rate of decoding by preventing inexact probability informationin the one or more low density parity check codes from beingconcentrated in a single area.
 58. An apparatus for recording opticalinformation recording, comprising: an encoding portion for encoding databy using one or more low density parity check codes; a light modulatingportion for representing data, which is encoded at the encoding portion,into a data page which is configured with a plurality of data blocks;and a beam source for projecting beam to the light modulating portion sothat the data page represented in the light modulating portion isrecorded at a recording medium as hologram, wherein the one or morelow-density parity check codes is divided into a plurality of segments,and wherein the plurality of segments are mapped with the data block todecrease the failure rate of decoding.
 59. The apparatus for reproducingoptical information of claim 58, wherein the data blocks include aplurality of subblocks, and wherein the one or more low density paritycheck codes is mapped among the subblocks.
 60. The apparatus forreproducing optical information of claim 59, wherein the one or more lowdensity parity check codes are scrambled.
 61. The apparatus forreproducing optical information of claim 59, wherein mapping theplurality of segments among the plurality of subblocks decreases thefailure rate of decoding by preventing inexact probability informationin the one or more low density parity check codes from beingconcentrated in a single area.